The Automobile Club de l’Ouest (ACO) and International Motorsports Association (IMSA) have announced that Xtrac will be the sole gearbox supplier for the new Le Mans Daytona hybrid race category known as ‘LMDh’. The ACO and IMSA together have unified this innovatory top-tier for both the WeatherTech SportsCar Championship in the USA and Fédération Internationale de l’Automobile (FIA) World Endurance Championship (WEC).
“It’s a visionary hybrid transmission built on years of experience gained by operating at the highest level of motorsport,” says Xtrac chief executive Adrian Moore. “Prototype gearboxes will be available from mid-2021 for hybrid system testing”.
The P1359 gearbox developed for the new LMDh class is a 7-speed transverse arrangement with an integrated motor-generator unit (MGU) driving into the gearbox through an optimised gear train. The integration of the hybrid system is a vital attribute of the LMDh specification. Xtrac has worked closely with the ACO, IMSA, Bosch and Williams Advanced Engineering (WAE) to ensure that the package, function, and overall operation is optimised for cost, weight, performance, and reliability. Bosch is supplying the MGU and hybrid control system, while WAE is supplying the battery system.
The new LMDh class has been created by the convergence of ACO and IMSA regulations to provide a cost-effective, high-performance car able to race in the WEC series as well as the IMSA sportscar championship in the USA. This cost capped sportscar will also share a common spine consisting of the complete car less the bodywork, engine, and hybrid system with the next generation LMP2 sportscar.
“The four appointed chassis suppliers, Dallara, Ligier, Multimatic and Oreca provided invaluable feedback to Xtrac during the design of the transmission,” says Moore. “It ensured that we met their requirements with a common transmission that will fit all chassis without modification. It was a vital goal to make sure we achieved the cost-effectiveness of this new class of race car”.
The P1359 gearbox uses Xtrac’s well-proven P1254 integrated valve actuator (IVA) gearchange system. It houses full form ground and Xtrem polished gears and shafts in a magnesium RZ5 casing, which is a structural part of the car taking all of the loads from the rear suspension and rear impact structure, rear wing, and safety wheel tethers.
The gearbox has a maximum combined internal combustion engine (ICE) and MGU power capability of 585kW (785bhp), with the engine speed operating within the range of 6,000 to 10,000 rpm. Each chassis builder can homologate its powertrain with specific gear ratios. The integrated MGU drives through a novel gear train homologated for each engine. It ensures that no matter what the maximum engine revs, the MGU is matched to the engine speed, thus ensuring that no engine gains an advantage; parity being the whole ethos behind the new class.
The gearbox also includes a limited-slip plate differential with an externally gas-charged pre-load and a semi-dry-sump oil system. Integral to the gearbox is a 3-litre engine oil catch tank which simplifies the powertrain installation, and the whole package including the MGU drive, but not including the MGU itself, weighs 78kg (172lb).
The P1359 gearbox, with its integrated hybrid system, is a critical new product for Xtrac. “We see the transition to electrified propulsion systems both on the road and the track,” says Moore. He’s proud that the company he helms is in the vanguard of technical developments designed to reduce the cost and environmental impact of essential future mobility systems. “We have compelling technology to help make motorsport even more relevant and exciting, which also influences the crucial evolution of the next generation of road cars.”